A contraction used to condense a six-word phrase (Do you know what I mean ?) into two syllables. Commonly used by those with limited vocabulary to confirm whether their audience is comprehending their babble-speak. Also used to convey excitement, disappointment, or anger about subject matter. Origin: 5 boroughs of NYC.

A'yo son, these chicks from Jersey be gettin' me tight for no reason, nah'mean ?

A shortened version of the phrase "Know what I mean".
Commonly used with males in the ages of 10-20. These males exhibit a need to be cool with the crowd. This can often work if the objected audience answers "yes".

However, caution should be used to avoid using the term "nah mean" when the answer will be "no". This can result in a loss of coolness, thus, defeating the purpose of the term "Nah mean".

Some have also given responses with N' mean. Shortened for the phrase "I know what you mean".

Martin: I hate it when I get killed so fast in Halo. Nah mean?
Andrew: N' mean.